An electro‐optical technique has been developed to measure high‐frequency electric fields in free space. Electrically induced birefringence in an electro‐optical crystal is used to modulate a linearly polarized continuous‐wave laser beam. The modulation impressed on the laser beam contains both frequency and field intensity information. A way to use this technique as both a frequency and power meter is discussed. A proof‐of‐principle experiment has been carried out with a 3.1‐GHz magnetron source.